Because of their unique sieving characteristics, as well as their catalytic properties, crystalline molecular sieves and zeolites are especially useful in applications such as hydrocarbon conversion, gas drying and separation. Although many different crystalline molecular sieves have been disclosed, there is a continuing need for new molecular sieves with desirable properties for gas separation and drying, hydrocarbon and chemical conversions, and other applications. New molecular sieves may contain novel internal pore architectures and acid site properties, providing enhanced selectivities and activities in these processes.
Molecular sieves are classified by the Structure Commission of the International Zeolite Association according to the rules of the IUPAC Commission on Zeolite Nomenclature. According to this classification, framework type zeolites and other crystalline microporous molecular sieves, for which a structure has been established, are assigned a three letter code and are described in the “Atlas of Zeolite Framework Types” Sixth Revised Edition, Elsevier (2007).
Molecular sieves are periodically ordered in three dimensions. Structurally disordered structures show periodic ordering in dimensions less than three (i.e., in two, one or zero dimensions). This phenomenon is characterized as stacking disorder of structurally invariant Periodic Building Units (PerBuU). Crystal structures built from Periodic Building Units are called end-member structures if periodic ordering is achieved in all three dimensions. Disordered structures are those where the stacking sequence of the Periodic Building Units deviates from periodic ordering up to statistic stacking sequences.
Molecular sieves having a MTT-type framework code have a one-dimensional 10-ring pore system. MTT-type molecular sieves have very similar, but not identical, X-ray diffraction patterns. SSZ-32 and its small crystal variant, SSZ-32x, are known MTT-type molecular sieves.
SSZ-32x, in comparison with standard SSZ-32, has broadened X-ray diffraction peaks that may be a result of its inherent small crystals, altered Argon adsorption ratios, increased external surface area and reduced cracking activity over other intermediate pore size molecular sieves used for a variety of catalytic processes. SSZ-32x and methods for making it are disclosed in U.S. Pat. Nos. 7,390,763, 7,569,507 and 8,545,805.
Known methods for making SSZ-32 and SSZ-32x employ high temperature calcination steps before the ion-exchange step for the purpose of removing extra framework cations. For Example, in Example 2 of U.S. Pat. No. 8,545,805, the as-made SSZ-32x product was calcined at 595° C. prior to undergoing ammonium ion-exchange. Likewise, in Example 2 of U.S. Pat. No. 7,390,763, the as-made SSZ-32x produce was calcined at 1100° F. (593° C.) prior to undergoing ammonium ion-exchange.
However, it has now been found that by using the manufacturing method described herein below, a novel molecular sieve designated herein as SSZ-95 is achieved. SSZ-95 is characterized as having a unique acid site density which causes the molecular sieve to exhibit enhanced selectivity, and less gas-make (e.g. production of C1-C4 gases), compared to conventional SSZ-32x materials.